Frictional losses in gear boxes are of significant interest to gear box designers as these losses transform into heat. The direct result is a reduction in the fuel efficiency of the vehicle involved. Further@ in many instances@ this heat has to be absorbed and dissipated so that lubricant properties and gear box performance are not significantly compromised. This effort is to measure and document the comparative friction losses in a gear mesh due to gear tooth surface condition and lubricant. Three distinct surface conditions are considered. They are ground@ Isotropic Superfinished (REM ISF?) and tungsten-incorporated diamond-like carbon coating (W-DLC). Two lubricants@ MIL-PRF-23699 and Mobil SHC 626 lubricants are considered. The experimental effort is conducted on a high speed@ power re-circulating (PC)@ gear test rig@ which had been specially instrumented with a precision torque transducer to measure input torque to the 4-square loop. The torque required to drive the loop is measured under various speeds and tooth loads within the torque loop@ with test gears with different surface conditions and with different lubricants. Two operating torque levels within the 4-square loop at speeds ranging from 4@000 rpm (pitch-line velocity of 19 m/sec) to 10@000 rpm (pitch-line velocity of 47 m/sec) are evaluated. Based on the collected data a qualitative analysis of the effect of gear tooth surface condition on frictional losses is presented. Further@ the surface characteristics of the tooth flanks of the ground@ superfinished and coated gears are also described.